Common Lisp the Language, 2nd Edition

28.1.2.1. Defining Classes

The macro defclass is used to define a new named class. The definition of a class includes the following:

• The name of the new class. For newly defined classes this is a proper name.

• The list of the direct superclasses of the new class.

• A set of slot specifiers. Each slot specifier includes the name of the slot and zero or more slot options. A slot option pertains only to a single slot. If a class definition contains two slot specifiers with the same name, an error is signaled.

• A set of class options. Each class option pertains to the class as a whole.

• Supplying a default initial value form for a given slot.

• Requesting that methods for generic functions be automatically generated for reading or writing slots.

• Controlling whether a given slot is shared by instances of the class or whether each instance of the class has its own slot.

• Supplying a set of initialization arguments and initialization argument defaults to be used in instance creation.

• Indicating that the metaclass is to be other than the default.

• Indicating the expected type for the value stored in the slot.

• Indicating the documentation string for the slot.